As is known, net elements are present on the market, used for the reinforcement, containment, stabilization and/or the consolidation of terrain.
A first example relates to a net element or grid structure made of a substantially flat plastic material. The element is stretched in the manufacturing process of the product in two directions such as to increase the structural strength thereof in both directions and the possibility of confining the meshes between the covering material. The shape of the product makes it suitable as a stabilizer or containing element or otherwise for use where an action of reinforcement and stabilization is required, substantially uniform in all directions of the lie plane of the net structure. It should be noted in fact that the openings in the grid, substantially square, to a certain extent enable interlocking with the granules present in the soil and the cooperation with the same.
The net element is obtained by subjecting the extruded or perforated product first to a stretching action in the longitudinal direction, with the passage of rollers rotating at different speeds, and then in the transversal direction via the action of an orthopedic implant for transverse stretching.
A second example concerns reinforcing structures made of a plastic material and composed of a reticular structure having a series of substantially stretched longitudinal elements and a series of transversal elements substantially not stretched. These elements create meshes with elongate apertures which can be inserted in the terrain to be strengthened during the depositing of the structures in place. The reinforcing structure is obtained by extrusion or perforation of sheets and then by stretching in the exiting direction from the extruder, and exhibits parallel longitudinal elements at a fixed distance and a length that is adjustable according to requirements. The reticular structure is in fact subjected to unidirectional stretching along the exit direction from the extruder, and then cut transversally; the grid thus obtained has a good tensile strength in the direction of the longitudinal elements, and the ability to contain and reinforce terrain. Note that the openings in the grid, of substantially rectangular shape, allow a certain amount interlocking with the granules present in the terrain and co-operation with them too, and the pronounced thickness of the non-stretched transversal elements ensures a good anchoring capability. It should however be noted that the orientation of the maximum resistance direction coincides with that of the exiting direction from the extruder and this entails major limitations at the level of application and implementation due to the limited dimension of the width of the finished product available today.
At present, in fact, the product reaches a maximum width of two meters and in existing applications, the task of laying the element along the direction to be reinforced means having to constantly repeat the process of sectioning the product into many strip such as to create panels in a sufficient number to match the dimensions of the work area, and then the panels have to be laid side by side.
A further drawback is that the existing panels are not interconnectable along the sides and therefore, in order to make the reinforcement continuous panels are partially overlapped, with an ensuing waste of material.
Also, the anchoring along the reinforcing direction is at present possible only along the ends of each panel which are of limited size and therefore not efficient for uses where it is necessary to cover areas of significant extension.
Further examples of net structures are described in documents U.S. Pat. Nos. 4,756,946, 4,374,798, 4,743,486, 5,269,631, 5,267,816 5,419,659, EPO418104A2, and U.S. Pat. No. 5,053,264.